From: Hugo Marrero <HMarrero@HBOI.edu>
Reply-To: personal_submersibles@psubs.org
To: "'personal_submersibles@psubs.org'" <personal_submersibles@psubs.org>
Subject: RE: [PSUBS-MAILIST] To Dan H. (or anybody with VBT (MBT)
knowledge)
Date: Wed, 5 May 2004 14:37:11 -0400
Hi all,
Ballasting a small shallow water sub proprely requires at least three
separate ballasting systems or techniques:
1- Main Ballast System (Also called Air Ballast)
2- Variable Ballast System (Also called Water Ballast)
3- Fixed Ballast System
The purpose of the first is to provide the freeboard necessary to keep the
hatch above water and is the system with the most buoyancy reserve of all.
It is the largest consumer of air in the sub.
The second is to accommodate for differences in payload from dive to dive,
the system capacity depends on the size constraints, weight and total
payload available. As a rule you never want to run your VBT system
completely full or completely empty. It should be designed so that the
system oprerates between 20% & 80% of it's range. The rest is designated as
a reserve buoyancy.
The third is either fixed by means of lead or syntactic foam in order to
adjust for the lack or excess buoyancy. It is normally set with a full
payload and the ballast system set at 80% of it's full capacity. It is also
designed to adjust the trim of the submersible with a full payload
condition
by distributing the lead throughout the length of the submersible.
In smaller subs the total payload must be calculated before each dive and
the fixed ballast adjusted accordingly in order to operate within the
parameters established.
This is the traditional method of ballasting subs, other subs like the
Deep
Flight depart from the norm and depend on speed, rudders and elevators to
submerge.
By the way, the term sinking implies a one way trip to the bottom. Subs
submerge and ascend, not sink and float... ;o)
Hugo